Change the fuel filter.

 

Not sure how experienced you are with Cummins motors But Be careful on the fuel screw. you could have a runaway. if you are experienced sorry for bringing it up

 

What is the most boost you see right now?

What are your EGTs when under load?

If i understood that correctly, Youre seeing 10 lbs of boost max, even under load. Check your fuel filter first, if that doesnt fix it next check for a boost leak. If that doesnt work slowly check over things to see if you can find problems

 

Check the high idle screw. Make sure that you are getting full travel on the throttle lever.